(1) Technical Field
The present invention relates to a field sequential liquid crystal display device capable of displaying color images, and the invention relates more specifically to an active matrix type liquid crystal display.
(2) Related Art
In recent years the active matrix liquid crystal display is being widely used for personal computers. It is not only used for the notebook type personal computers but also for the desktop personal computers with a large screen.
The active matrix liquid crystal display used on personal computers are required to display a plurality of information at one time and also to have a capability of full-color display at high definition level and with high quality.
The conventional active matrix color liquid crystal display forms a color image by passing white light through red, green and blue color filters provided over each of pixels. Hence, in the conventional active matrix color liquid crystal display, the resolution will be reduced to one third of that of the actual active matrix liquid crystal display. For example, an active matrix liquid crystal display having (640×3×480) pixels can only produce an image corresponding to the resolution of VGA standard, which is (640×480). An active matrix liquid crystal display with (800×3×600) pixels can only display an image corresponding to the resolution of SVGA standard, which is (800×600). Hence, to produce an image corresponding to high resolution requires three times the number of pixels.
To solve the problem described above, a study has been conducted recently on a method different from the conventional color display method. This driving method, called a field sequential driving method, divides one frame of image into three subframes and turns on red, green and blue backlights each for one-third frame duration to display an image corresponding to that color for one-third frame duration.
FIG. 22 is a timing chart of the conventional field sequential driving method. The timing chart of the conventional field sequential driving method in FIG. 22 shows a start signal for writing a video signal (Vsync signal), turn-on timing signals (R, G and B) for red, green and blue LEDs, and a video signal (VIDEO). Tf represents a frame period. TR, TG and TB represent durations in which red, green and blue LEDs are lit, respectively.
A video signal supplied to the liquid crystal panel, for example R1, is obtained by compressing an original red video signal entered from outside to one-third in the time axis direction. A video signal supplied to the liquid crystal panel, for example G1, is obtained by compressing an original green video signal entered from outside to one-third in the time axis direction. A video signal supplied to the liquid crystal panel, for example B1, is obtained by compressing an original blue video signal entered from outside to one-third in the time axis direction.
In the conventional field sequential driving method, the R, G and B LEDs are turned on successively during their corresponding LED turn-on periods TR, TG and TB. During the red LED turn-on period (TR), a red video signal (R1) is supplied to the liquid crystal panel to write one screenful of a red image on the liquid crystal panel. During the green LED turn-on period (TG), a green video signal (G1) is supplied to the liquid crystal panel to write one screenful of a green image on the liquid crystal panel. During the blue LED turn-on period (TB), a blue video signal (B1) is supplied to the liquid crystal panel to write one screenful of a blue image on the liquid crystal panel. These three screenfuls of image written into forms one frame.
The color display based on the conventional field sequential driving method has three times the resolution of the conventional color display. With this conventional field sequential driving method, however, because red, blue and green images are each displayed once for one-third the duration of one frame, the flicker of the screen becomes a very serious problem. Because of the flicker, the user cannot stand many hours of use of the display.
The present invention has been accomplished in view of the above-mentioned drawback and its object is to provide a display capable of minimizing the flicker and having a high resolution.